[A case of Infective Endocarditis Caused by Pseudoclavibacter species]

Infective endocarditis is an infectious disease usually caused by bacteria, including streptococci, staphylococci, and enterococci. In this report, a case of infective endocarditis in which Pseudoclavibacter spp. detected as the causative agent was presented. A 66-year-old female patient was admitted to our hospital with weight loss, malaise, and lumbar pain. A 2/6 murmur was detected in the physical examination of the patient, who had a history of mitral valve surgery nine years earlier. Blood sample was collected for culture and vancomycin [1 g/24 hours, intravenously (IV)] and gentamicin (80 mg/8 hours, IV) therapy were started. Gram-positive bacilli were detected on the second day of incubation in the blood culture bottle incubated in the BacT/ALERT 3D microbial detection system (bioMerieux, France). High uptake in the focal area of the mitral valve on positron emission tomography-computerized tomography (PET-CT) was interpreted as infective endocarditis. The patient was considered to be at very high risk for surgery and she was discharged after the vancomycin treatment completed for 42 days. For bacterial identification, DNA was isolated using a commercial kit (Invitrogen PureLink Genomic DNA Mini Kit; ThermoFisher Scientific, Waltham, MA, USA), and the 16S rRNA gene was amplified by a polymerase chain reaction (PCR) assay using universal primers 27F and 1492R. Sequence analysis of the PCR product was carried out on an Applied Biosystems 3730XL DNA Analyzer with an Applied Biosystems BigDye Terminator v3.1 Cycle Sequencing Kit (ThermoFisher Scientific, Waltham, MA, USA). A 1366 bp long sequence of the isolate was analyzed using the Basic Local Alignment Search Tool (BLAST) in GenBank and the sequence was 99% compatible with Gulosibacter spp. (GenBank sequence ID: LR884222.1, identity 1365/1366 bp) and Pseudoclavibacter spp. (GenBank sequence ID: FJ375951.1, identity 1364/1366 bp). Upon the negative result of nitrate reduction test of bacterium that was oxidasepositive, the bacterium was considered as Pseudoclavibacter spp. Linezolid, clindamycin, and tetracycline susceptibilities were determined by using the disc diffusion method. The isolate was susceptible to linezolid and resistant to clindamycin and tetracycline. It was also susceptible to penicillin [minimum inhibitory concentration (MIC) = 0.002 µg/ml], vancomycin (MIC= 0.25 µg/ml), and rifampicin (MIC= 0.003 µg/ml) and was categorized as "susceptible, increased exposure" to ciprofloxacin (MIC= 0.25 µg/ml), as determined by using a gradient strip test. Pseudoclavibacter species are non-spore-forming, non-motile, catalase-positive, aerobic gram-positive bacilli belonging to the Microbacteriaceae family. A limited number of clinical cases due to Pseudoclavibacter species have been reported. In the present case, gram-positive bacilli were considered to be the causative agent of infective endocarditis because of the growth of the same bacteria in six bottles of blood cultures taken at different times and increased focal involvement on PET-CT. To our knowledge, this is the second reported case of infective endocarditis due to Pseudoclavibacter species. In conclusion, in cases of clinical compliance in patients with prosthetic heart valves, gram-positive bacilli should be considered causative agents of infective endocarditis and in such cases, a range of microbiological assays should be used for identification.